The present invention relates to methods and apparatus for dual containment of piped substances. The invention more particularly relates to piping systems constructed of flanged concentric pipe segments and having an interior plastic liner to protect the segments from corrosive piped substances. The invention permits fluids, which may leak from the inner shell of a concentric or dual-walled pipe segment, to be detected before escape of the fluid into the environment. The invention features a connector that provides a secure and reliable seal between connected pipe segments and enables leak detection monitoring to be conducted at such connection points. The invention also features a novel concentric-type pipe segment design having an annulus, a flange which presents an exterior axial flanged face, and an aperture communicating the annulus with the exterior flange face. The aperture is adapted to transmit fluid which has leaked from the inner shell of the pipe segment into communication with a connector which adjoins the exterior flange face.
Many facilities which handle hazardous or caustic chemicals cannot permit even tiny amounts of piped substances to escape without risking significant health or environmental consequences. Accordingly, a number of apparatuses and techniques have been suggested for containing and detecting leaks in piping systems. Some of these suggestions have involved the use of concentric pipe segments. One such suggestion, for instance, features a piping system of flanged concentric pipe segments in which the segments have an interspace defined between the inner and outer segments. Leak detection fittings are positioned along outer pipe segments which permit monitoring of escaped material into the interspace. This type of piping system may include a passage extending through the flange of a pipe segment, whereby leakage between flanges of abutting pipe segments may be flushed from the passage. Inner and outer O-ring seals on the flanges may be used to bracket the entrance to the passage along the flange face.
Hazardous chemical piping systems also exist which employ rigid mating of adjacent components. Connectors are used which essentially transmit the entire bolt torque load from joined flanges of two pipe elements across a single metal ring. Such a system may permit higher bolt torque loads to be used in connecting the elements than other systems. However, the rigid mating of this system is vulnerable to vibration-induced fatigue and failure over time.
Although such systems facilitate control of leaks from piping system segments, they do not facilitate active monitoring of leaks at flanged connection points. In fact, it is at connection points that leakage is oftentimes most likely to occur. The escaping fluid can also breack outer O-ring seal and thereby result in fluid reaching the environment before it can be detected. This is a distinct possibility when the fluid is especially corrosive. O-ring seals, as well as rigid matings, at connection points also tend to fail or weaken when subjected to vibration, repeated temperature changes, impacts, fire, or other hazards.
In another background aspect it is noted that, while alternative piping systems exist which offer dual containment layers along the length of the pipe segments, these systems provide only a single acceptable fluid seal at leakage-prone flanged connection points. The absence of a second reliable seal against leaks belies such a system's claim of providing true dual containment. Clearly, systems that provide true dual containment and facilitate meaningful leak detection are desirable.